Simultaneous bi-directional signaling describes a signaling technique that transmits bits simultaneously, in both directions, over a single transmission line. Bi-directional signaling makes uses of the capability of wires to transmit waves in both directions. In contrast, transmitting data in only a single direction avoids full use of the bandwidth available over a single transmission line. As such, in simultaneous bi-directional signaling circuits, bits travel in one direction on a forward-traveling wave and in the other direction, on a reverse traveling wave.
Accordingly, transmitted waves within a bi-directional signal circuit are transmitted in both directions, at the same time, resulting in the formation of a wave on the transmission line, which is a superposition of the forward and reverse traveling waves. As a result, the effective wire density and pin count of a system can be doubled by sending bits simultaneously in both directions over a transmission line using simultaneous bi-directional signaling. As an example, a simultaneous bi-directional signaling circuit 100 is depicted in FIG. 1.
As depicted in FIG. 1, bits within the bi-directional signaling circuit 100 travel to the right from transceiver A 110 to transceiver B 130 and are encoded on a forward traveling wave. Conversely, bits traveling to the left from transceiver B 130 to transceiver A 110 are encoded on the reverse traveling wave. Accordingly, the voltage on the transmission line 120 is a superposition of the forward and reverse traveling waves. Consequently, in order to reconstruct or recover a received signal, for example at transceiver A 110, the receiver 116 constructs a copy of the forward traveling wave and subtracts this wave from the transmission line voltage in order to recover the received data.
As a result, a conventional bi-directional signaling circuit 100 utilizes a subtraction circuit 114/134 in order to recover received data. Unfortunately, the requirement of a subtraction circuit within bi-directional signaling circuits, such as depicted in FIG. 1, result in low power and inefficient area usage. In addition, such techniques are not always compatible with advance communication techniques, such as channel filtering and multi-level signaling. In addition, the use of subtraction circuits and replica drivers will lead to lower bandwidths of input/output (I/O) links in future products.
In other words, the limitations describe above are due to the fact that conventional simultaneous bi-directional signaling circuits utilize analog means, such as subtractors and replica drivers, in order to recover a received inbound wave from the superposition of the forward and reverse traveling waves. Therefore, there remains a need to overcome one or more of the limitations in the above-described, existing art.